Fellmongering industries have as their objective the treatment of skins in order to produce on the one hand bare skins (sometimes designated by "pelts") intended for the manufacture of leathers by tawery, and on the other hand the wool which is called upon to undergo various treatments up to spinning.
Two essential types of method are at present employed in these fellmongering industries; these methods consist in a first phase in preparing the skins by steeping and picking operations and then in a second phase in ensuring an attack upon the roots of the hairs of the wool with a view to weakening their resistance and finally in a last phase, in carrying out the operation proper of stripping the wool from the skins (still designated by "unhairing"), which consists in tearing the hair from the skin.
The preparatory operations common to the two methods comprise a first steeping which is put into effect by stacking the skins upon one another and immersing these stacks in steeping tanks and then a picking operation intended for removing the impurities contained in the wool, and finally a second steeping similar to the first. These operations last about 48 hours.
In one of the methods, the older one, the second phase is carried out by a process of bacteriological fermentation the average duration of which is of the order of 4 days. Under these conditions, taking into account operations of preparation, the duration of a wool-stripping cycle in this type of method is of the order of one week and this duration is one of the essential disadvantages of this method.
In the other method the second phase consists in impregnating the flesh side of the skins by means of a solution having a base of sodium sulphide, and in stacking the skins on pallets and leaving them to stand like that for about 8 to 12 hours in order to allow diffusion of the sulphide through to the hair side. This method with sulphide thus offers the advantage of considerably shortening the duration of the wool-stripping cycle.
However, the sulphide method as employed at present has a number of serious disadvantages. In the first place the complete cycle which lasts about 60 hours remains long and it would be highly desirable to shorten it in order to make more profitable use of the materials and to reduce the necessary storage areas; in addition the quality of the skins and the wools obtained is generally mediocre and very uneven from one skin to another. That is, during the course of the skins' standing in the form of a stack on the pallets the wool inevitably becomes soiled by the sulphide which causes a more or less marked degradation of it; again, the skins situated on top of each stack are subjected to a sulphide action of shorter duration than the skins situated below; that is, the skins on the top are the last to be put into place on the stack and the first to be removed. As a consequence these skins (known as white skins) are difficult to strip of their wool because of a too superficial action of the sulphide, whereas the skins below (known as black skins) have undergone too powerful an attack, bringing with it risks of degradation of the wool and a blackening of certain zones of them which then lowers the quality of the leathers manufactured from them.
The present invention proposes to indicate a method of treatment employing sulphide like the known method but exempt from the aforesaid defects of this method.
It is aimed essentially at indicating a method the duration of implementation of which is considerably shortened and which enables skins and wools to be produced which profit by a good quality which is uniform for all of the skins.
Another objective of the invention is to reduce the personnel necessary for a given production whilst making the work much less arduous for the labour force.
Another objective is to provide a treatment unit which enables implementation of the said method under the most profitable conditions.